1. Field of the Invention
The present invention relates to a chemical vapor deposition apparatus and a chemical vapor deposition method. More particularly, it is concerned with a chemical vapor deposition apparatus wherein a feed gas is introduced at a gas introduction portion of a horizontal tubular reactor which is arranged such that the direction of the feed gas to be fed in the horizontal tubular reactor is made substantially parallel to a substrate, so that semiconductor films are subjected to uniform chemical vapor deposition on a heated substrate; and a chemical vapor deposition method by the use of the above-mentioned apparatus.
2. Description of the Related Arts
There has been a rapid increase in recent years, in demands for a gallium nitride compound semiconductor to be used as a device for a light emitting diode, laser diode, and the like concentratedly in the field of optical communication. There is known, for instance, as a process for manufacturing a gallium nitride compound semiconductor, a process in which a semiconductor film of a gallium nitride compound is subjected to chemical vapor deposition on a substrate of sapphire or the like which has been set in advance in a tubular reactor so as to form an objective film by using, as a group III metal source, an organometallic gas such as trimethylgallium, trimethylindium and trimethylaluminum and by using ammonia as a nitrogen source.
In addition, there is available, as an apparatus for manufacturing the above-mentioned gallium nitride compound semiconductor, a chemical vapor deposition apparatus comprising a horizontal tubular reactor equipped with a susceptor for mounting a substrate thereon, a heater for heating the substrate, a feed gas introduction portion arranged such that the direction of the feed gas fed in a tubular reactor is made parallel to the substrate, and a reaction gas exhaust portion. The chemical vapor deposition apparatus comprising the horizontal tubular reactor is of such constitution that the substrate is placed on the susceptor in the tubular reactor, the substrate is heated, and thereafter a gas containing a feed gas is supplied in the reactor in the direction parallel to the substrate so that a semiconductor film is subjected to chemical vapor deposition to form a film on the substrate.
However, in such a horizontal tubular reactor, since the tubular reactor wall in opposition to the substrate is heated to a high temperature, there are caused such problems that the feed gas undergoes thermal decomposing reaction in the vicinity thereof, decomposed products or reaction products are deposited on the tubular reactor wall, and the deposited solid is dropped on the substrate, thereby markedly deteriorating the quality of the crystal. Accordingly, it is necessary to clean the inside of the tubular reactor at every time of chemical vapor deposition being performed. Consequently, the above-mentioned chemical vapor deposition apparatus comprising a horizontal tubular reactor has usually suffered from poor productivity.
In order to solve such problems, there have recently been developed an improved apparatus and method for chemical vapor deposition wherein a forcing gas introduction portion is placed on the tubular reactor wall in opposition to the substrate, a forcing gas not affecting the reaction of a carrier gas, etc. is supplied inside the tubular reactor in the direction perpendicular to the substrate so as to prevent thermal decomposing reaction of the feed gas from occurring in the vicinity of the tubular reactor wall in opposition to the substrate. It is said that the improved apparatus and method make it possible to prevent decomposed products or reaction products from being deposited on the tubular reactor wall without exerting adverse influence on the chemical vapor deposition of the semiconductor film on the substrate by properly and optionally controlling the flow rate of the forcing gas in accordance with the kind and flow rate of the feed gas, temperature of the heated substrate and the like.
Nevertheless, with regard to the above-mentioned method and apparatus which prevent decomposed products or reaction products from being deposited by supplying a forcing gas from the tubular reactor wall in opposition to the substrate, gas streams which cross at right angles, that is, a gas containing the feed gas and the forcing gas are mixed with each other on the substrate, and thus are more prone to be disordered, whereby the streams are often difficult to control. For instance, in the case of carrying out chemical vapor deposition of a large-size substrate or simultaneously conducting that of a plurality of substrates, it is difficult to supply a feed gas in a uniform concentration over a wide range of the substrate. Moreover, in the case of carrying out chemical vapor deposition by using the foregoing trimethylgallium, trimethylindium or trimethylaluminum as a feed gas, the necessity for a high temperature of 1000xc2x0 C. or higher as the substrate heating temperature leads to formation of an intricate gas streams on the substrate, therefore it is difficult to control such gas stream.
In general, a relatively small amount of a forcing gas based on a gas containing a feed gas makes it impossible to prevent decomposed products or reaction products from being deposited, whereas a relatively large amount of a forcing gas based thereon exerts a negative influence upon the chemical vapor deposition of semiconductor films on the substrate.
Under such circumstances, an object of the invention is to provide a method and an apparatus for chemical vapor deposition that are capable of assuring high quality crystals in the use of a horizontal tubular reactor without generating a deposit of decomposed products or reaction products on tubular reactor walls in opposition to a substrate even in the case of carrying out chemical vapor deposition of a large-sized substrate or simultaneously conducting that of a plurality of substrates, or performing the same at a high temperature.
Other objects of the invention will become obvious from the text of this specification hereinafter disclosed. In such circumstances, intensive research and development were accumulated by the present inventors in order to solve the above-described problems involved in the prior arts. As a result, it has been found that in regard to chemical vapor deposition by using a horizontal tubular reactor which supplies a gas containing a feed gas in the direction parallel to a substrate and supplies a forcing gas in the direction perpendicular to the substrate, gas flow control is facilitated, whereby a deposit of decomposed products or reaction products on tubular reactor walls can be prevented, without exerting evil influence upon the chemical vapor deposition of semiconductor films on the substrate, by a method in which the flow rate of the forcing gas in the central portion of a forcing gas introduction portion is made lower than in the peripheral portion of the forcing gas introduction portion, or an alternative method in which the flow rate of the forcing gas in the middle of a feed gas passageway is made lower than at both the end portions of the above-mentioned passageway, even in the case of carrying out chemical vapor deposition of a large-sized substrate or simultaneously conducting that of a plurality of substrates, or performing the same at a high temperature. Thus, the present invention has been accomplished by the foregoing findings and information.
That is to say, the present invention relates to a chemical vapor deposition apparatus for a semiconductor film, which comprises a horizontal tubular reactor equipped with a susceptor for mounting a substrate thereon, a heater for heating the substrate, a feed gas introduction portion arranged such that the direction of a feed gas supplied in the tubular reactor is made substantially parallel to the substrate, a reaction gas exhaust portion, and a forcing gas introduction portion on a tubular reactor wall in opposition to the substrate, wherein the flow rate per unit area of a forcing gas which is supplied from the forcing gas introduction portion into the tubular reactor is made lower in the central portion of the forcing gas introduction portion than in the peripheral portion of the forcing gas introduction portion.
In addition, the present invention pertains to a chemical vapor deposition apparatus for a semiconductor film, which comprises a horizontal tubular reactor equipped with a susceptor for mounting a substrate thereon, a heater for heating the substrate, a feed gas introduction portion arranged such that the direction of a feed gas supplied in the tubular reactor is made substantially parallel to the substrate, a reaction gas exhaust portion, and a forcing gas introduction portion on a tubular reactor wall in opposition to the substrate, wherein the flow rate per unit area of a forcing gas which is supplied from the forcing gas introduction portion into the tubular reactor is made lower in the middle of a feed gas passageway than at both the end portions of said passageway.
Further, the present invention is concerned with a chemical vapor deposition method which comprises mounting a substrate on a susceptor for a horizontal tubular reactor, heating the substrate with a heater, supplying a gas containing a feed gas in the direction substantially parallel to the substrate, supplying a forcing gas from a forcing gas introduction portion placed on a tubular reactor wall in opposition to the substrate so as to subject a semiconductor film to chemical vapor deposition on said substrate, and which further comprises making the flow rate per unit area of the forcing gas that is supplied from the forcing gas introduction portion into the tubular reactor lower in the central portion of the forcing gas introduction portion than in the peripheral portion of the forcing gas introduction portion.
Furthermore, the present invention is related to a chemical vapor deposition method which comprises mounting a substrate on a susceptor for a horizontal tubular reactor, heating the substrate with a heater, supplying a gas containing a feed gas in the direction substantially parallel to the substrate, supplying a forcing gas from a forcing gas introduction portion placed on a tubular reactor wall in opposition to the substrate so as to subject a semiconductor film to chemical vapor deposition on said substrate, and which further comprises making the flow rate per unit area of the forcing gas that is supplied from the forcing gas introduction portion into the tubular reactor lower in the middle of a feed gas passageway than at both the end portions of said passageway.